Back in the 1980s I found, bought, restored and used a 1920 ABC.
Here are some recollections and observations on this amazing if under-developed motorcycle.
The bike, when found, was very original and unmolested but had not run in many years. It was covered in surface rust but none serious. From a photo that I had, taken in the Sopwith factory in Christmas 1919, of the first batch for sale to the public, I was able to identify the front tyre as an original North British Clincher tyre in white rubber with a very distinct snowflake-shaped tread pattern which indicated to me a fairly low mileage bike.
When stripped down for restoration, I found no serious wear and the only thing that I replaced was one of the gearbox bearings. The pistons were interesting for the large amount of skirt clearance needed as these were very early aluminium pistons made before low expansion alloys were invented.
On stripping down the final drive, I found behind the sprocket, a large screwed ring with peg spanner holes. These holes had been greatly abused by someone with a hammer and punch.
On removal of this ring, the final drive bevel gears, with chipped teeth on the outer edges of the gears, were revealed. The screwed ring was the mesh adjustment for the bevel gears and Granville had not thought to provide this with any means of locking so had continuously unscrewed itself until the gear teeth started missing each other, hence all the hammer marks and chipped teeth as the frustrated owner had to stop every few miles to tighten up the mesh of the bevels. A simple locking plate was made by which provided a complete cure.
An interesting single-lever Claudel Hobson automatic carburettor was fitted which worked well but, as il was a long way from the cylinder beads, had to be provided with an exhaust-heated muffle around the manifold to prevent icing, Gasses tapped-off the silencer where led up to the muffle to heat it and then out the other side to atmosphere. Because the gas outlet was at a similar level to the inlet, the condensate could gather in the muffle and sit there causing corrosion of the manifold. The addition of a drain at the lowest point completely cured the problem.
The kick-starter was never going to work. It is wrong on so many levels and needed a redesign so I just bump-started it, which is very easy to do, as it is very light.
The dynamo drive was a bit odd as well. The drive was taken off the output of the gearbox and so was dependant on road speed to balance the load, but I suppose there was not much traffic then.
I considered the lubrication system was a bit hit-and-miss. It relied on crankcase depression to pull oil through the Enots drip-feed regulator on the tank top. I added a Pilgrim pump which I drove from the front of the camshaft and mounted on the timing cover, which worked well.
They had a reputation for loosing pushrods which flew off into the ditch, never to be seen again. My ABC had its original rocker set-up and I never lost a pushrod in 3.000 miles.
I used the ABC for about three years and covered about 3,000 miles on it with complete reliability, mostly with my then girlfriend on the pillion. On a long weekend trip on the VMCC’s Bromyard to Bangor run, we were clocked by someone with a chronometric accurate speedo cruising at 70mph and latter that weekend, we climbed the fearsome Bwlch y Groes pass in Snowdonia in 2nd gear. All this on a 1920 motorcycle of only 400c carrying a combined weight of about 20 stone.
I consider the ABC to be a work of genius, at least 20 years ahead of the rest at the time.
It’s a pity that its production coincided with the rampant inflation following the first world war, which led to its rapidly increasing price, which perhaps let Sopwith to rush out with premature sales.
From “Roadholder 419 November 2022” - written by Dave Rosser – Courtesy of Phil Batten